The present invention relates to a heat-shrinkable laminated film comprising a mixed resin layer (A) of a polyamide resin (hereinafter referred to as "Ny resin")and a saponified ethylene-vinyl acetate copolymer (hereinafter referred t as "EVOH resin") at a specific mixing ratio and a layer (B) containing an EVOH resin, the thickness of the layer (A) being larger than that of the layer (B), and a process for producing the heat-shrinkable laminated film. More particularly, the present invention relates to a heat-shrinkable laminated film comprising at least two layers of a mixed resin layer (A) consisting essentially of 65 to 85 wt% of an Ny resin and 15 to 35 wt% of an EVOH resin and a layer (B) containing at least 55 wt% of an EVOH resin, he thickness of the layer (A) being larger than that of the layer (B), and a process for producing the heat-shrinkable laminated film.
Most of fatty foods such as raw meats and processed meats have irregular shapes and are not uniform in size. For packaging such foods having various shapes a shrink-packaging method using heat-shrinkable films is industrially adopted. General procedures of this method comprises the steps of inserting an object into a bag of a film, removing the air from the bag under vacuum, sealing the opening of the bag, and heating the bag so as to heat-shrink the film, and conforming an closely contacting the film with the content, thereby obtaining a fine package. In this method, the heat-treatment also serves to sterilize the content and is ordinarily carried out at a temperature of 80.degree. to 100.degree. C.
A film used for such shrink packaging must be excellent in gas-barrier property and conformable adhesiveness, and be sufficiently shrunk when heated with hot water or hot air of 80.degree. to 100.degree. C.
As such a shrink-packaging film, an EVOH resin film having a high gas-barrier property is considered to be suitable. However, since an EVOH resin film having an excellent gas-barrier property is inferior in low-temperature stretchability, such resin cannot be said to be suitable for practical use.
To eliminate this defect, various methods have been proposed.
For example, a heat-shrinkable film having a mixed resin layer of an EVOH resin and a Ny resin [Japanese Patent Application Laid-Open (KOKAI) Nos. 54-16576 (1979) and 58-36412 (1983)], a heat-shrinkable laminated film composed of an EVOH resin layer and a Ny resin layer [Japanese Patent Application Laid-Open (KOKAI) No. 56-136365 (1981)], and a heat-shrinkable film comprising a mixed resin layer of an EVOH resin and a Ny resin, and a thermoplastic resin layer laminated on the mixed resin layer so as to provide a heat-sealing property [Japanese Patent Application Laid-Open (KOKAI) No. 56-15326 (1981)]have been proposed.
However, a film having a mixed resin layer of an EVOH resin and a Ny resin as the barrier layer has an insufficient gas-barrier property for the film required to have a high gas-barrier property, or when a higher stretching film-forming property is necessary, such a film cannot always be said to satisfy the stretching film-forming property.
Accordingly, a film having a layer containing an EVOH resin as the main constituent and showing both high gas-barrier property and excellent stretching film-forming property is now in demand.
As a result of the study by the present inventors in order to improve the stretching film-forming property of an EVOH resin while maintaining a high gas-barrier property, it has been found that a heat-shrinkable laminated film having both high gas-barrier property and excellent stretching film-forming property are obtained by laminating a layer containing an EVOH resin with a mixed resin layer of an EVOH resin an a Ny resin, and more particularly, by laminating a resin layer comprising an EVOH resin and a Ny resin at a specific mixing ratio and having a thickness larger than a layer containing an EVOH resin with the layer containing an EVOH resin and the thus obtained laminate is easy to orient. The present invention has been achieved on the basis of this finding.